1. Field of Invention
The present invention relates to an apparatus and a method for inputting input key signals for an optical disk player. More particularly, the present invention relates to an apparatus and a method for inputting input key signals for an optical disk player using an analog voltage input signal.
2. Description of Related Art
The fabrication of a chip has become much more complex because of the development of semiconductor technology. The density of logic gates in a chip is rapidly increasing due to the improvements of semiconductor processes. A single chip now can accomplish functions previously requiring a plurality of chips. This is what is called system-on-chip (SOC).
However, the area of a chip may be very large if this chip has to provide many functions. More area means more cost. Additionally, I/O (input/output) among modules in the chip becomes very complex. If more inputs and outputs of the chip are intended, the fabrication and packaging cost may increase and difficulty in testing the chip is foreseeable. How to reduce the total of a chip I/O now becomes an important issue since those chip designers endeavor to reduce both the cost and area of a chip.
Reducing the number of chip I/O not only reduces the cost, but also reduces the design complexity of the circuit board of the chip. Chip designers have more flexibility when designing if the number of circuit paths on their chip circuit board is more less than before. The electromagnetic interference between different circuit paths can also be lowered.
An important issue is that many systems use keys as an interface for communicating with a user. The circuit paths used to connect the keys and send signals from the keys will occupy a large space even those functions of the keys are simple. Thus, an approach for reducing and simplifying the chip I/O is needed.
FIG. 1 is a circuit diagram illustrating a traditional solution for inputting key signals into a chip. With reference to FIG. 1, keys 102, 104, 106, and 108 are used to send control signals to a chip 112. The chip 112 has four input pins 120, 122, 124 and 126 for receiving signals. The key 102 has a conducting status and a breaking one. When a switch 130 of the key 102 is pressed, a reference voltage 110 connects to the input pin 120 electrically such that the voltage value on the input pin 120 is equal to the reference voltage 110. When the switch 130 is released, the input pin 120 is grounded through a resistor 114, and the voltage value of the input pin 120 is down to zero. According to the same operation way, the release/connection statuses of the keys 104, 106, and 108 incorporate with resistors 116, 117, and 118 determine the voltages on input pins 122, 124, and 126.
The circuit diagram shown in FIG. 1, includes four input statuses accomplished by 4 keys. Logic 0 and 1 are indicated if a key is released and pressed, respectively. The chip 112 then determines the key statuses by detecting logic 0 or 1 delivering from related input pins. In other words, the chip 112 receives input key signals from the keys 102, 104, 106, and 108 through 4 input pins 120, 122, 124, and 126. When there are too many input pins, both the chip area and manufacturing cost increases significantly. There is a need to disclose a chip having less I/O pins so as to reduce manufacturing cost and chip size simultaneously.